A conventional differential gearing for vehicle is known as having a construction as disclosed in Japanese Registered Utility Model No. 2520728, for example. This differential gearing for vehicle of the prior art will be briefly described with reference to FIG. 31. It is to be noted that reference characters for the conventional construction shown in FIG. 31 will be indicated in parentheses in this specification. Formed in a differential case (12) are a pinion gear receiving opening (14) and an axle receiving opening (16) which extend orthogonally to each other. Left and right side gears (20L, 20R) are disposed within the differential case (12) so as to be axially movable therein and are splined to left and right axles (22L, 22R), respectively which are inserted into the axle receiving opening (16). Sliding members (24) of a smaller diameter than the side gears (20L, 20R) are disposed between the back surface (20a, 20a) of the left and right side gears (20L, 20R) and the internal surface of the differential case (12).
Also disposed within the differential case (12) is a pinion gear (26) having substantially the same diameter as the pinion gear receiving opening (14) and rotatable supported therein in meshing engagement with the left and right side gears (20L, 20R). A pinion gear holding plate (28) is fitted over the external diameter of the pinion gear (26), which is prevented from being removed from the case (12) by a snap ring (30) which is fitted into a groove (12a) in the differential case (12). A pinion shaft (32) is passed through the pinion gear (2) in alignment with the axis thereof to prevent its tilting.
To assemble the differential gearing for vehicle constructed in the manner mentioned above, the sliding members (24) and the left and right side gears (20L, 20R) are assembled from the outside of the differential case (12) into the differential case (12) through the pinion gear receiving opening (14). The pinion gear (26) is then assembled into the pinion gear receiving opening (14) from the outside of the differential case (2) in which the side gears (20L, 20R) have been assembled so as to mesh with the latter. At this time, the pinion shaft (32) is previously disposed within the differential case (12) so that the pinion gear (26) can be passed over the pinion shaft (32). After the pinion gear (26) has been assembled into the pinion gear receiving opening (14), the pinion gear holding plate (28) is fitted, which is then prevented from being removed by the snap ring (30).
The conventional construction mentioned above is subject to various problems as mentioned below.    1. Because the pinion gear is carried by the differential case only over an area located outward of the meshing engagement with the side gears, there remains a problem that when a torque is applied to the differential case, the pinion gear may be tilted in the circumferential direction, causing a likelihood of a biased abutment to induce an abrasion.    2. Because the side gears are inserted into the differential case through the pinion gear receiving opening, it is impossible to choose a diameter of the side gears which is greater than the diameter of the pinion gear. It is also necessary to insert one of the side gears initially before the other side gear is inserted, and this prevents a spacing between the side gears from being reduced. Consequently, the gearing requires an increased size and involves an increased rotational backlash.    3. Because the pinion holding plate (locking washer) which prevents a removal of the pinion gear is planar, there results a problem that when a force is applied to the pinion gear to cause to be displaced, there occurs a change in the center-to-center distance with respect to the side gear to produce a displacement in a meshing position.    4. Because the side gears are relatively small while the pinion gear is relatively large as mentioned above, the peripheral speed during the rotation increases as a result of an increased diameter (external diameter) of the pinion gear to enhance a thermal expansion thereof, producing a likelihood of causing a seizure. To avoid this problem, it is necessary to increase a clearance, resulting in an increased amount of the backlash as mentioned previously.    5. When the pinion gear increases in size, it is susceptible to the influence of a centrifugal force, producing a variation in the differential action limiting force, and this produces a problem that a change in the performance is likely to occur.
This invention is proposed to cope with these problems, it is an object of the present invention to provide a differential gearing for vehicle which is capable of suppressing a tilting of a pinion gear if a differential case rotates to apply a force upon the pinion gear, thereby maintaining an appropriate action while suppressing a biased abrasion of sliding parts.    PATENT REFERENCE 1: Japanese Registered Utility Model No. 2520728